Digital testing is a necessary component of the manufacturing of digital devices. Testing helps in ensure the functionality of devices while it reduces the probability of shipping faulty products, which would result in a return and reduction in customer satisfaction. As a result, digital testing is performed on almost all digital devices. While digital testing is a necessary step of the manufacturing process, it is in general slow. Therefore, testing can add a significant amount of time and expense to the manufacture of a digital device.
A seemingly ubiquitous device in today's world is a wireless communications device. From cellular telephones, cordless phones, wireless communications and data networks, pagers, etc., wireless devices have become a part of everyone's way of life. For these wireless devices, a crucial test that they all should undergo is a bit-error-rate (BER) test. The BER test determines the rate of faulty bits to transmitted bits. A wireless device with a high BER will sound poorly (if it is a communications device) or perform poorly with a low data rate (if it is a data device).
The BER test is achieved by pushing a known data stream through the wireless device, typically via the antenna, and then comparing the data stream prior to a decoding stage with a copy of the known data stream. Errors, if any, are counted. If the BER for the device exceeds a predetermined amount, the device is deemed as having failed the BER test. The BER test can and is performed on wired devices as well.
A difficulty associated with performing the BER test is aligning the known data stream with the data stream from the device prior to a decoding stage. This is due to delays introduced into the test system by the testing hardware and the device itself. To make the matters more difficult, the delays can vary depending on different test systems and different devices. Therefore, there is not a constant amount of delay that can be readily compensated.
One common way to perform the BER test is to save the data stream produced by the device into memory and then the two data streams are compared via a software program. The software program performs a correlation between the two data streams to synchronize the two streams prior to comparing them. Unfortunately, a software implementation of the BER test is extremely slow. Its inherent lack of speed tends to either shorten the BER test being performed or to reduce the number of devices tested. Neither is a viable option for producing a device with low failure rates.
Another way to perform the BER test is to use hardware to perform the comparison. However, due to the varying delay between test systems and devices, it is extremely difficult to develop a hardware based BER test system that is flexible to test devices with varying delays.
A need has therefore arisen for a BER test system that can accommodate the varying delays seen between different test systems and devices and at the same time provide a short testing time that will be conducive to the more complete testing of a larger number of devices.